Aluminum member

ABSTRACT

An aluminum member produced by casting a molten metal composed of predetermined ingredients is disclosed. The aluminum member is casted by supplying the molten metal to a space between a fixed die, a movable die, and a sand core disposed between the fixed die and the movable die, and then cooling the molten metal moderately.

FIELD OF THE INVENTION

The present invention relates to an aluminum member, particularly, to a large aluminum cast part.

BACKGROUND OF THE INVENTION

Aluminum cast parts are widely used in practical fields for the object to reduce weight. Further, aluminum members produced by die casting are widely provided to achieve fine grain size (for example, see JP 2541412 B1).

JP 2541412 B1 provides an aluminum alloy for die casting including magnesium (Mg), silicon (Si), iron (Fe), and manganese (Mn) within certain ranges. The alloy is used for the material of electronic devices such as computers.

The technique discussed in JP 2541412 B1 is useful for small thin parts such as electronic devices. For parts with a large difference in thickness such as vehicle parts, there occurs a difference in cooling rate between a thick portion and a thin portion.

Aluminum-manganese (Al-Mg) materials generally have low fluidity and is difficult to cast. When such material having low fluidity is used for a large part with a large difference in thickness, a misrun or insufficient supply of molten metal during solidification might cause cracks.

To avoid such problem, an aluminum-silicon (Al-Si) based materials are used, although the Al-Si based material requires heat treatment to obtain strength, which may results in high production cost.

Since weight reduction is desired for vehicles and the like, it is required to produce parts with low cost by aluminum casting also for a large part with a large difference in thickness.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a technique that enables production of an aluminum cast part also for a large part with a large difference in thickness.

According to the present invention, an aluminum member composed of ingredients of, by weight percentage, 1.0% to 3.0% of Si, 4.0% to 6.0% of Mg, 1.0% or less Fe, 1.0% or less Mn, 0.5% or less Cu, 0.5% or less Zn, at least either of 0.10% to 0.20% of titanium (Ti) or 0.0015% to 0.0030% of beryllium (Be) added to obtain a fine grain size in a metal structure, and a residual of Al and inevitable impurities is provided. The aluminum member is produced using a cast die and a sand core disposed in the cast die by casting a molten metal composed of the aforementioned ingredients in a space between the cast die and the sand core.

In the present invention, Si is included in the aluminum cast part within a range from 1.0% to 3.0%. If the included Si is less than 1.0%, the 0.2% proof strength and the tensile strength are reduced, and if the included Si is more than 3.0%, elongation is reduced. If the included Si is within 1.0% to 3.0%, predetermined degrees of 0.2% proof strength, tensile strength and elongation can be secured. Further, fluidity of Al-Mg based alloys, which is the negative aspect, can be improved by adding Si.

Although when the included Si is within 1.0% to 3.0%, the molten aluminum alloy has a disadvantage in fluidity, and when high pressure casting (die casting) is applied for a large part with a large difference in thickness, a misrun at a portion to be filled in the final stage of casting or a crack at a thick portion and a thin portion may occur.

In view of such problem, in the present invention, a sand core having a low heat conductivity is disposed in a die to suppress the dropping of temperature of a molten metal and also to reduce the difference in thickness of the part.

In the present invention, the hollow structure produced by using the sand core can provide a thin light structure having high rigidity.

Thus the present invention provides a technique that can produce an aluminum cast part also for a large part with a large difference in thickness, that is, a part that should have a large difference in thickness if a core is not used when producing the part.

The aluminum member is preferably a hollow die cast member produced by high pressure casting. Thus, a thin aluminum member can be provided, and moreover, since a high pressure casting is used, a fine grain sized aluminum member having high strength can be provided.

The hollow die cast member is desirably used for a subframe for a vehicle. The hollow die cast member can be made thin and has superior mechanical property without treatment, and therefore is preferable for a subframe requiring strength and reliability. Thus, a light and low cost subframe can be provided. The subframe supporting a power plant such as engines receives rotational forces and vibration generated by the power plant and loads from a suspension, and therefore requires high strength and high rigidity.

Preferably, a cross-member unit and a suspension supporting unit are integrated in the subframe for a vehicle and both the members have a hollow structure.

The subframe for a vehicle preferably includes an inclined portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a general concept of die casting apparatuses;

FIG. 2 is a perspective view illustrating a vehicle front structure;

FIG. 3 is a bottom view of a subframe;

FIG. 4 is a sectional view of the subframe;

FIGS. 5A to 5C illustrate a relationship between the added amount of Si and tensile strength, 0.2% proof strength, and elongation; and

FIG. 6 illustrates a relationship between the existence of a sand core and a flow length.

DETAILED DESCRIPTION OF THE EMBODIMENT

An embodiment of the present invention will be described in detail with reference to the accompanying drawings.

EMBODIMENT

A conventional die casting apparatus 100 is described as a comparative example in FIG. 1A. A molten metal 105 is injected through a sleeve 104 into a cavity 103 formed by a fixed die 101 and a movable die 102. The cavity 103 is made large to produce a large thick part. Note that, although the general concept and the cavity 103 with a constant thickness is illustrated in FIG. 1A, an actual part may have a large difference in thickness. In a case where a molten metal 105 having poor fluidity is injected, when the difference in thickness is large, the difference in cooling rate between the thick portion and the thin portion may cause casting defects.

As illustrated in FIG. 1B, a die casting apparatus 10 according to an embodiment of the present invention includes, for example, a base plate 11, a fixed plate 12 fixed on the base plate 11, a fixed die 13 attached on the fixed plate 12, a movable plate 14 arranged to oppose the fixed plate 12, a die-closing cylinder 15 that moves the movable plate 14, a movable die 16 attached on the movable plate 14, a sand core 17 disposed between the movable die 16 and the fixed die 13, a cylindrical sleeve 18 attached to the fixed plate 12, and a plunger 19 that moves the sleeve 18 along the axial direction.

Further, the sand core 17 is coated with an alumina coating applied by sintering a mixture of natural sand and artificial sand so that the sand core 17 can be used for high pressure injection.

The fixed die 13 and the movable die 16 constitute a cast die 20.

A runner 22 and a plurality of gates 23 are provided in the fixed die 13. These gates 23 are opened to the cavity 24 located between the sand core 17 and the fixed die 13. By providing the sand core 17, the thickness T of the cavity 24 is made thin.

A molten aluminum alloy 26 (hereinafter abbreviated as molten metal 26) is injected into the sleeve 18 through a pouring gate 25 provided on the sleeve 18. The molten metal 26 is kept in the sleeve 18. By moving the plunger 19 forward, the molten metal 26 is injected into the runner 22 with high pressure, and then through a plurality of gates 23, the molten metal 26 is injected into the cavity 24 with high pressure.

During injection, the outer surface of the molten metal 26 is cooled by the fixed die 13 and the movable die 16, and the inner surface of the molten metal 26 is cooled by the sand core 17. Because the sand core 17 has very poor property to work as a coolant than a metal core, the molten metal 26 is cooled moderately. Since the cooling is moderately performed, the fluidity of the molten metal 26 is kept for a relatively long period of time, allowing the molten metal 26 to reach the far end of the cavity 24 without solidifying.

After the molten metal 26 is solidified, the die-closing cylinder 15 moves the movable plate 14 and the movable die 16 to open the die. The aluminum casting is taken out from the opened cast die 20.

The sand core 17 is taken out of the aluminum casting and a hollow die cast member composed of an aluminum member is obtained.

Note that, FIG. 1B merely illustrates an example. The cast die 20 can be rotated by 90 degrees so that the sand core 17 can be horizontally positioned. Further, the runner 22 may be provided inside the fixed die 13.

In FIGS. 2 and 3, the arrow Fr indicates the front side and the arrow Rr indicates the rear side.

As illustrated in FIGS. 2 and 3, the vehicle front structure 30 includes right-and-left side frames 31R and 31L (R is appended to indicate the right side, and L is appended to indicate the left side, as will be similarly used hereinafter) arranged along the front-and-rear direction of the vehicle body, a subframe for a vehicle 40 (hereinafter referred to as subframe 40) attached below the right-and-left side frames 31R and 31L, right-and-left suspension arms 32R and 32L provided on the right-and-left end portions of the subframe 40, and right-and-left suspensions 33R and 33L connected to the right-and-left suspension arms 32R and 32L, respectively.

The vehicle front structure 30 further includes a steering gear box 34 attached to the upper portion of the subframe 40 and a torque rod 36 that connects the subframe 40 and the power plant 35.

A steering wheel 39 is attached to the steering shaft 38 extending from the steering gear box 34.

For example, the power plant 35 is configured by integrating an engine and a transmission, that is, as an engine/transmission unit, and is arranged along the right-and-left direction between the right-and-left side frames 31R and 31L.

As illustrated in FIG. 3, the subframe 40 is configured with right-and-left suspension supporting units 41R and 41L supporting the suspension arms 32R and 32L and a cross-member unit 42 that extends between the suspension supporting unit 41R and the suspension supporting unit 41L. The suspension supporting units 41R and 41L and the cross-member unit 42 are integrally formed and each has a hollow structure.

As illustrated in FIG. 4, the subframe 40 has an inclined portion 43 that inclines from the rear side to the front side of the vehicle so as to avoid interference with the power plant (see reference sign 35 in FIG. 3). Since the inclined portion 43 gradually changes the shape, the fluidity is preferably maintained.

The whole structure of the subframe 40 is formed in a hollow die cast member produced by high pressure casting using the sand core (see reference sign 17 in FIG. 1B). The sand core contributes to moderate the cooling to produce a thin structure. The reference sign 45 indicates a large hollow space formed by the sand core.

In FIG. 3, the sand core is located inside each of the suspension supporting units 41R and 41L and the cross-member unit 42. In this manner, larger portion can be cooled moderately and thereby a thin structure can be produced.

The ingredients of the molten metal 26 shown in FIG. 1B are, by weight percentage, 1.0% to 3.0% of Si, 4.0% to 6.0% of Mg, 1.0% or less Fe, 1.0% or less Mn, 0.5% or less Cu, 0.5% or less Zn, at least either of 0.10% to 0.20% of Ti or 0.0015% to 0.0030% of Be added to obtain a fine grain size in a metal structure, and a residual of Al and inevitable impurities. Among the above-mentioned ingredients, description will be made for Si below.

As illustrated in FIG. 5A, the included Si of 2.0% by weight percentage gives the highest tensile strength and the included Si of 3.0% gives the second highest tensile strength, followed by the included Si of 1.0%.

As illustrated in FIG. 5B, the 0.2% proof strength increases proportional to the added amount of Si.

As illustrated in FIG. 5C, the included Si of 1.0% gives the highest elongation and the included Si of 2.0% gives the second highest elongation, followed by the included Si of 3.0%.

That is, if the included Si is less than 1.0%, the tensile strength is small, and if the included Si is more than 3.0%, the elongation is small. If the included Si is within 1.0% to 3.0%, the predetermined degrees of tensile strength, proof strength, and elongation can be maintained.

Now, description is made for the sand core.

The flow length in the apparatus illustrated in FIG. 1A and the flow length in the apparatus illustrated in FIG. 1B are investigated.

As illustrated in FIG. 6, when the molten aluminum is 5% Mg-2% Si, the apparatus using the sand core has a far longer flow length than the apparatus that does not use the sand core.

The aluminum member according to the embodiment of the present invention is applicable for any hollow casting and can be produced by die casting, sand mold casting, low pressure casting, and other casting methods.

Although the aforementioned embodiment is applied to the subframe for a vehicle, the embodiment may be applied to other vehicle structural members such as suspension arms, frame members of motorcycles, and components of structures other than those for vehicles. 

What is claimed is:
 1. An aluminum member composed of ingredients of, by weight percentage, 1.0% to 3.0% of Si, 4.0% to 6.0% of Mg, 1.0% or less Fe, 1.0% or less Mn, 0.5% or less Cu, 0.5% or less Zn, at least either of 0.10% to 0.20% of Ti or 0.0015% to 0.0030% of Be added to obtain a fine grain size in a metal structure, and a residual of Al and inevitable impurities, wherein the aluminum member is produced using a cast die and a sand core disposed in the cast die by casting a molten metal composed of the ingredients in a space between the cast die and the sand core.
 2. The aluminum member according to claim 1, being a hollow die cast member produced by high pressure casting.
 3. The aluminum member according to claim 2, wherein the hollow die cast member is a subframe for a vehicle.
 4. The aluminum member according to claim 3, wherein a cross-member unit and a suspension supporting unit are integrated in the subframe for a vehicle, the cross-member unit and the suspension supporting unit having a hollow structure.
 5. The aluminum member according to claim 3, wherein the subframe for a vehicle includes an inclined portion. 